In many situations it is either desirable or necessary to remove sludge and other similar materials from a liquid reservoir. For example, in settling ponds such as settling ponds used in piggeries, dairies, poultry farms, animal feed lots as well as in sewerage settling ponds or other ponds, there is, over a period of time, an increase in solid matter in the pond water due to building up of sludge and sediment. As a result of build up of this material, it is necessary to empty the pond at regular intervals to allow removal of the sludge or solid matter. This firstly creates an environmental problem in liquid disposal during draining of the pond. After draining of the pond, heavy machinery is then required to be used at considerable cost to remove the solid matter or sludge which has settled on the base of the pond and then spread or arrange the solid matter or sludge for drying.
In some of the above types of pond, in particular sewerage settling ponds or lagoons, a membrane cover is provided over the pond to eliminate odour and trap methane. This not only reduces the greenhouse gas emissions but also provides a source of energy as the methane gas may be used to fire gas engines to generate electricity. In these types of pond, the gas impervious membrane cover is placed over the pond and anchored and sealed around the edges of the pond so that methane gas generated in the pond is trapped and can be drawn off when required for use.
Ponds and lagoons provided with a membrane cover of this type present particular difficulties when sludge is required to be removed from the pond. The cover is required to be lifted or removed to allow machinery to access the pond however in these circumstances, the collected methane is obviously lost thereby creating greenhouse gas problems and in addition loss of an energy resource. The disadvantages of sludge removal as referred to above are also encountered.